Unlike most aspects of health insurance, there are very few regulations for insurance companies when determining what they consider reasonable or customary. In fact, only a few states even define what constitutes the terms "reasonable, usual and customary" and even fewer have regulations on the methodology used in determining these charges. Some insurance companies use statistics found in national studies of your geographic area in order to determine reasonable and customary charges. These studies include the fees charged by medical service providers such as doctors and hospitals. However, in some cases, insurance companies determine these charges using information compiled by themselves and regulated by no one.